In fabricating high signal-to-noise ratio (SNR) magnetic recording media, it is desirable that the magnetic particles or grains of the magnetic layer(s) be of uniformly small size, with a small, uniform amount of exchange coupling between the magnetic particles or grains. The optimal value of the exchange coupling is different for longitudinal, perpendicular, tilted, and heat-assisted magnetic recording media, e.g., a higher exchange coupling is desired for perpendicular media. However, in each instance a constant small value of exchange coupling between neighboring magnetic particles or grains is desired.
A low value (i.e., small amount) of exchange coupling between neighboring magnetic particles or grains is desired in order that magnetic switching of the magnetic particles or grains does not become too highly correlated. Reducing the exchange coupling decreases the sizes of the magnetic particles or grains, i.e., the sizes of the magnetic switching units. The cross-track correlation length and media noise are correspondingly reduced. However, near-zero exchange coupling between magnetic particles or grains produces a very low squareness-sheared M-H hysteresis loop, a broad switching field distribution, decreased resistance to self-demagnetization and thermal decay, and low nucleation fields (Hn) in perpendicular media designs. Non-uniform exchange coupling allows some magnetic particles or grains to act independently, with small particle or grain size, while other magnetic particles or grains act in clusters, resulting in broad distributions of particle or grain size and anisotropy field.
Heretofore, exchange coupling between neighboring magnetic particles or grains has been controlled by preferentially forming non-ferromagnetic material(s) at the boundaries between the magnetic particles or grains. Such non-ferromagnetic material may be formed during the sputter deposition of CoCrPtB-containing magnetic alloys on high temperature substrates by preferential surface diffusion of Cr and B atoms to the grain boundaries. The concentration of Co atoms varies between the centers of the magnetic particles or grains and the boundaries, such that a transition from magnetic to non-magnetic composition occurs. Exchange coupling in such compositionally segregated media is typically controlled by changing process parameters such as the Cr and B concentrations of the sputtering target and the substrate temperature during deposition.
Non-ferromagnetic material can also be formed at the boundaries between magnetic particles or grains during sputter deposition of CoPt-containing magnetic alloys on low temperature substrates by incorporation of a metal oxide material in the CoPt-based sputter target or by reactive sputtering of the target in a sputter gas containing oxygen (O2). Exchange coupling in magnetic media produced thereby is controlled by changing process parameters such as the sputter gas pressure, O2 concentration in the sputter gas, and oxide content of the sputter target.
In each of the above-described instances, the sputter deposition parameters are adjusted/selected such that the amount of non-ferromagnetic material present at the boundaries between the magnetic particles or grains is sufficient to effect significant, but not complete, decoupling of the magnetic exchange between the particles or grains.
However, a problem associated with the above-described method/procedure for effecting exchange decoupling is that the magnetic exchange between a pair of magnetic particles or grains is extremely sensitive to, thus dependent upon, the arrangement of a very small number of atoms. As a consequence, the amount of exchange coupling between pairs of magnetic particles or grains exhibits considerable variation, whereby some particles or grains are more strongly coupled than others.
Another problem associated with the above-described method/procedure for effecting exchange decoupling is that radial diffusion profiles of the atoms of the segregated elements (Cr and B) or molecules (e.g., metal oxides) depend upon the sizes of the magnetic particles or grains. Consequently, the larger magnetic particles or grains can have a systematically different composition than the smaller particles or grains, and therefore a systematically different amount of exchange coupling and magnetic anisotropy.
Still another problem associated with the above-described methodologies is that the composition of the entire film, including the ferromagnetic particles or grains, the weakly exchange coupled ferromagnetic regions between neighboring magnetic particles or grains, and the exchange decoupling non-ferromagnetic regions between neighboring magnetic particles or grains is substantially the same, except for the preferential transport (i.e., diffusion) of certain atomic species (e.g., Cr and B) or molecules (metal oxides). Changing the amount of exchange coupling in the magnetic film or layer generally changes the composition of the magnetic particles or grains in addition to that of the boundary material. Thus, it is difficult to separately optimize the properties of each component of the magnetic film or layer.
In view of the foregoing, there exists a clear need for improved methodology for fabricating high performance, high SNR magnetic recording media which avoids or otherwise obviates the above-described disadvantages, drawbacks, and problems associated with the conventional methodology and facilitates fabrication of improved high performance magnetic recording media, including longitudinal, perpendicular, tilted, and heat-assisted media.
The present invention, therefore, addresses and solves the above need for improved methodology for fabricating high performance, high SNR magnetic recording media with enhanced magnetic characteristics, while maintaining full compatibility with all aspects of conventional automated manufacturing technology for fabrication of magnetic recording media, e.g., hard disks. Moreover, the inventive methodology can be readily implemented in a cost-effective manner comparable with that of existing manufacturing methodologies.